A Marine-led U.S. relief operation in the Philippines ramped up Tuesday, as typhoon survivors in remote areas struggled through a fourth day without food or potable water, medical care or shelter from the rain.

Two more ships with advanced medical capabilities, tracked vehicles and other disaster response equipment have been ordered from Japan to the Philippines, U-T San Diego has learned.

The amphibious dock landing ships Ashland and Germantown are slated to leave Sasebo, Japan, Wednesday morning. After picking up Marine landing teams in Okinawa, the ships should arrive in the Philippines within a week.

Along with the aircraft carrier George Washington and six escort ships already steaming toward the Philippines, “between all of them they do bring a very considerable and robust medical capability to the mission,” said Navy Capt. Darryn James, chief spokesman for Pacific Fleet.

“Our number one goal is to assist the government of the Philippines to ease the suffering of those devastated by this typhoon. So we are considering all options to assist,” he added.

One option is deployment of the San Diego-based Navy hospital ship Mercy, which James said is in a "reduced operating status" and would require additional time to reach the disaster area. The Mercy visited the Philippines in June 2012 for the annual Pacific Partnership humanitarian and disaster relief exercise.

The Defense Department is continuing to work closely with the Philippine government to determine what, if any, additional assets may be required, Marine officials said.

Initial response

Meanwhile, American military aircraft have been ferrying supplies and refugees across the ravaged central islands of the archipelago, which are plagued by outbreaks of diarrhea and the stench of rotting bodies.

Nearly 250 U.S. troops have converged on the islands, including about 180 Marines. The 3rd Marine Expeditionary Brigade based in Okinawa, Japan, is leading the effort, working with the Philippine government and its armed forces, other U.S. government agencies and civilian aid organizations.

More troops are on the way with the George Washington and its carrier strike group expected to arrive from Hong Kong within about two days.

As of Tuesday night, air crews aboard Marine MV-22 Osprey tiltrotors and KC-130J airplanes had delivered more than 107,000 pounds of food, water, and other emergency supplies provided by the Philippine government and the U.S. Agency for International Development, the Marines said.

They also evacuated more than 160 refugees from the Tacloban area where the typhoon hit hardest.

Authorities estimate that between 4.5 million to 9 million people were affected by the typhoon, which is called Yolanda in the Philippines. About 1,800 bodies have been recovered but more than 10,000 are feared dead.

Marine Brig. Gen. Paul Kennedy, commander of the U.S. military relief operation, said the city of Tacloban looked like it had been flattened by a 50-mile wide tornado.

"There's a lot we can do," Kennedy said. "We're working hand-in-hand with the Philippines, both with their armed forces and the national police. We will help them in their time of need."

But Kennedy also pleaded for more help, saying basic supplies for shelter, sanitation, food and water are urgently needed.

"The rest of the world needs to get mobilized, the rest of the donor community," he told NBC News. "A week from now will be too late. "

Marines

The Marine contingent is scheduled to grow to about 2,000 in coming days.

In addition to evacuating refugees, the Marine air crews have also transported more than 140 relief workers and other passengers in the storm-ravaged area. That mission is slated to continue Wednesday as MV-22 Osprey transport military assessment teams from Cebu to Tacloban.

Crews aboard four Ospreys and five KC-130J aircraft will also continue to evacuate refugees and ferry relief workers and humanitarian goods.

On Monday, the U.S. government announced it was dispatching $20 million in humanitarian aid to feed storm survivors and prevent illness.

A USAID shipment of emergency shelter materials and hygiene supplies such as soap and toilet paper for 10,000 families is expected to arrive in Manila early this week, followed in coming days by a second of equal size.

USAID is also sending more than 60 tons of emergency food products this week, including enough nutrition bars and paste to feed 20,000 children and 15,000 adults for about five days.

The hybrid Osprey, with its ability to land like a helicopter in austere areas but fly like a plane, "greatly enhances the Marine Corps' ability to respond rapidly and flexibly in this type of situation," said Col. Brad S. Bartelt, U.S. Marine Corps Forces, Pacific spokesman.

"The extended range and speed of a fixed wing aircraft allows us to respond more quickly and efficiently in a crisis situation."

The Marine Corps is keen to highlight the capabilities of the Osprey for maritime and island operations. The arrival of the first Osprey in Okinawa in August was met by protests, because of safety concerns stemming from the aircraft's troubled development and longstanding tensions between Marine Air Station Futenma and residents of the heavily populated area.

After a crash killed 19 Marines in 2000 in Marana, Ariz., the aircraft was redesigned. Today it is considered one of the safest rotary aircraft in the U.S. military.

Navy

The aircraft carrier George Washington and its crew of about 5,000 sailors can generate 400,000 gallons of drinking water per day. It also carries more than 80 aircraft, including 11 helicopters useful for transporting people and supplies in a disaster area.

"The capability to produce drinking water on such a scale is significant," said Bartelt. "Being able to provide this most basic of life support will have a dramatic impact on those affected by this storm."

The San Diego-based cruiser Cowpens is among the six other Navy ships ordered Monday afternoon to the Philippines, all of which can generate drinking water. The Cowpens left San Diego on Sept. 17 for a six-month tour in the 7th Fleet area of operations. Cruisers typically deploy with about 330 personnel.

“Cruisers can provide lift support … using embarked helicopters to take water, food, and supplies in areas that fixed-wing assets can't go. We are positioning assets in the region to support the armed forces of the Philippines if needed,” said Naval Surfaces Forces spokesman Lt. Rick Chernitzer.

The other ships heading for the Philippines are the cruiser Antietam, the destroyer Mustin, the destroyer Lassen, the destroyer McCampbell, and the supply ship Charles Drew, which is laden with food, water and other emergency supplies.